Conventionally, as a means typical of a PVD process for forming a thin film, there is a so-called ion plating process which includes generating a high-frequency electromagnetic field between a source of evaporation and an object to be vapor-deposited (substrate) to ionize substances evaporated in an active gas or an inert gas to perform vacuum vapor deposition. Also, a DC ion plating process which applies a d.c. voltage between a source of evaporation and an object to be vapor-deposited is proposed in Published Examined Patent Applications Nos. 29971/1977 and 29091/1977, etc. According to these methods, the surface of a substrate which is an object to be vapor-deposited is cleaned and activated by ion impact and the adhesion of a film formed is high. However, these methods have the drawback that in order to obtain predetermined ionization, a certain quantity of active or inert gas must be introduced into a vacuum tank and the quality of the resultant thin film is not so good.
In contrast, a CVD process is capable of forming a film by using a relatively simple installation compared to the PVD process and has strong reactiveness. However, the substrate must be raised to a predetermined temperature, so that this method cannot be applied to a substrate, for example, of plastics having no thermal resistance.
A first object of this invention has been made in view of the above and is to provide a new thin-film forming apparatus which is capable of forming a thin film efficiently.
A second object of this invention is to provide a thin film forming apparatus which is applicable to a substrate, for example, of plastics having no thermal resistance.
A third object of this invention is to provide a thin film forming apparatus which is not influenced by an electric field which varies depending on the shape of a source of evaporation or thermal electrons produced from the source of evaporation.